In general, sulfur-containing functional groups (sulfide, polysulfide, sulfone, sulfoxide, and the like) possess high molar refraction, and this is exhibited as an improved refractive index of a sulfur-containing polymer as compared to a polymer which does not contain sulfur. It is generally known that as sulfur content increases, a refractive index of a polymer increases, but a material with high sulfur content exhibits a low solubility in an organic solvent and thus it is difficult to be processed. Further, sulfur poisoning referring to inactivation of a metal catalyst caused by a sulfur-containing material in a process using the metal catalyst has been known, and, thus, it is very restricted to select a polymer polymerization catalyst that makes a minimum side reaction with a sulfur-containing compound.
Organic polysulfanes, covalent compounds with the general structure of R—Sn—R (n=1, 2, 3. . . ), are among the organic materials with the highest sulfur contents due to the presence of consecutive S—S bonds. These compounds are known for their involvement in various important chemical conversions and their interesting biological characteristics including antibacterial and cytotoxic activities.
Polymers containing linear polysulfanes in the main chain have been used as macro chain transfer agents in radical polymerization, stabilizing agents against PMMA, and are also regarded as promising materials for applications in dynamic covalent bond chemistry. Moreover, with the recent concerns regarding a rising global excess sulfur production and the emergence of the direct utilization of elemental sulfur in preparation of advanced materials as an active area of research, polysulfanes (some of which are obtained directly from reactions of elemental sulfur) are of interest from both environmental and economic perspectives.
Despite numerous studies on the synthesis and properties of polysulfane-containing polymers, applications have been very limited. High sulfur-content polymers are insoluble and lack processability, and their soluble, lower sulfur-content counterparts show that they are unstable towards nucleophiles, notably phosphines, even at room temperature. Furthermore, the S—S bond dissociation energy decreases with the increasing number of sulfur atoms in a polysulfane, making polysulfane-containing polymers prone to thermal degradation at a relatively low temperature. Particularly, controlling high molar refractive indices thereof and a modified polymerization method for preparing polymers containing polysulfane moieties are demanded, but the low bond dissociation energy is a problem to a radical polymerization method.
Further, the instability of polysulfane against phosphine requires a polymerization catalyst which does not contain phosphine. Therefore, a preparation method for modifying polysulfane-containing polymers into processable forms is a very challenging problem from both perspectives of solubility and stability of a product.
In this regard, Korean Patent Laid-open Publication No. 2000-0022993 discloses a sulfur-containing (thio)ether (co)polymer, and an optical element and a plastic lens manufactured using the same.